Tertiary amine oxides, Polonovski reactions, acetic anhydride

Polonovski Reaction. In the Polonovski reaction, tertiary amine oxides react with acetic anhydride to give the acetamide of the corresponding secondary amine (eq 34). 

POLONOVSKI REACTION. Demethylation of tertiary (or Heterocyclic) amine A-oxides on treatment with acetyl chloride or acetic anhydride 1o give A-acylated secondary amines and formaldehyde, along with (9-acylated aminophenols as a result of a side reaction. 

The use of a-cyanoamines in place of their less stable iminium ion precursors often results in high product yields in the Pictet-Spengler and other ring closure reactions. Thus, the Polonovski-derived a-cyanoamine (39a) cyclized to (40) in 84% yield, whereas reaction of the tertiary amine (39b) with mercury(n) acetate was unsuccessful (equation 13). The conversion of unstable S,6-dihydropyridinium salts (41), obtained by reaction of tetrahydropyridine IV-oxides with trifluoroacetic anhydride, into the stable, synthetically versatile tetrahydropyridine-2-carbonitiile (42) is another area in which use of this methodology has met with particular success (equation 14). ... 

Polonovski reaction. This reaction consists in the reaction of the N-oxide of a tertiary amine (1) with acetic anhydride to form the N-acylated secondary amine (2) as the major product and the deaminated ketone (3) as minor product ... 

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